The Relationship Between the ACTN3 Genotype and Measures of Stress, Exercise Performance, and Body Composition: A Pilot Trial

The purpose of this study was to assess the relationship between the expression of the ACTN3 gene (RR homozygous or RX heterozygous) and measures of stress, performance (i.e., bench press strength and endurance), and body composition. Strength was determined via a 1-RM (onerepetition maximum) for the bench press, and muscular endurance was determined by the number of repetitions to failure that were performed on the bench press at 60% of 1-RM. Body composition was assessed via a dual-energy X-ray absorptiometry (DXA). One hundred and five subjects completed the study ([mean ± SEM]: body weight: R/- group: 73.8 ± 1.7 kg vs. XX group: 66.6 ± 2.8 kg). There were no significant differences between XX and R/- (carriers of ACTN3) for fat mass, lean body mass, % fat or body weight. However, R/- demonstrated significantly greater bone mineral content (mean ± SEM: R/- = 2951 ± 70 g, XX = 2622 ± 73 g) and density (R/- = 1.35 ± 0.02, XX = 1.28 ± 0.03 g/cm 2). No differences were found for any of the other parameters.